Articles molded from aromatic polycarbonate resins are known to be unsatisfactory for use in hot, humid environments which include not only conditions of boiling water but also steam sterilization. (See C. A. Pryde et al, Polymer Eng. Sci., 22, 370 (1982); A. Ram et al, Poly. Eng. Sci., 25, 535 (1985); C. A. Pryde et al., J. Appl. Polym. Sci., 25, 2573 (1980); R. J. Gardner et al, J. Appl. Polym. Sci., 24, 1269 (1979); J. W. Shea et al, SPE 35th ANTEC, p. 326, Montreal, April, 1977 and L. M. Robeson et al, J. Appl. Polym. Sci, 28, 2925 (1983)). This is thought to be due to molecular weight reduction of the polycarbonate resin as a result of hydrolysis of the carbonate links in the polycarbonate and microcavity formation (specifically with multi-cycle steam sterilization conditions) which leads to structural flaws in the articles. On the other hand, articles molded from poly(aryl ether) resins have demonstrated excellent hydrolytic stability and therefore have utility in hot, humid environments including long term boiling water and multi-cycle steam sterilization.
One approach recently taken to improve the hydrolytic stability of articles molded from aromatic polycarbonate resin was to modify the polycarbonate resin by introduction of aromatic ester units (e.g., poly(ester-carbonates)). However, articles molded from poly(ester carbonate) resin are also significantly poorer in hot water and steam environments than articles molded from poly(aryl ether) resins. (See L. M. Robeson et al, paper presented at 2nd Annual Medical Plastics Conference (SPI), Washington, D.C. Sept. 10-11, 1984). However, slight improvements in the hydrolytic stability of articles molded from poly(ester carbonate) resin have been shown over articles molded from polycarbonate resin in steam sterilization environments presumably due to the higher glass transition temperature of the poly(ester carbonate) resin.
Blends of polyarylethers and polycarbonates are known from U.S. Pat. No. 3,365,517. The patent states that as a result of this blend, polycarbonate polymers are rendered more resistant to environmental stress crazing and cracking and their heat distortion temperatures are increased, and that thermoplastic polyarylene polyethers are rendered more resistant to thermal stress embrittlement.
However, this patent does not disclose or suggest that blends of poly(aryl ether) resins and polycarbonate resins can be used to form shaped articles which when exposed to moisture have improved hydrolytic stability.